This invention relates to marine propulsion engines such as outboard motors and the exhaust and control systems therefor.
Outboard motors present a number of challenges to the designer. The prime reason for this is the very compact nature of an outboard motor. An outboard motor generally includes a powerhead that consists of a powering internal combustion engine and a surrounding protective cowling. A drive shaft housing and lower unit depends from the powerhead. This drive shaft housing and lower unit journals a drive shaft that is driven by the engine and a transmission which drives a propulsion device in the lower unit for propelling an associated watercraft.
One of the prime design considerations and problems in connection with outboard motors is the provision of an adequate exhaust system that permits relatively free breathing, good silencing and also which ensures that excess heat is not generated which can be transmitted to the other components of the outboard motor.
The silencing presents a significant problem in that the length of the exhaust system is substantially limited by the compact nature of the structure. Generally, it has been proposed to utilize one or more expansion chambers generally formed in the drive shaft housing and lower unit for assisting in the silencing of the exhaust gases.
It is also a practice in outboard motor construction to discharge the exhaust gases to the atmosphere through the body of water in which the watercraft is operating, at least under higher speeds of travel. By utilizing this under water exhaust gas discharge, the silencing of the exhaust gases can be augmented.
However, the use of the under water discharge provides certain problems in that there is a concern that water may be ingested into the engine through the exhaust system. This is a particular problem in connection with two cycle engines because of the firing impulses and the existence of negative pressures in the exhaust under some circumstances.
It has been proposed, therefore, to employ a trap arrangement that will assist in insuring against ingestion of water into the engine through the exhaust system.
Also, in the interest of obtaining a good exhaust emission control, catalysts have been proposed for use in the exhaust system. The catalyst, however, should be protected from the water so as to avoid damage. This presents other problems in connection with location of the components. It has been proposed also to position the catalyst at an upstream location from the trap device so as to insure its protection from water.
U.S. Pat. Nos. 5,556,311, 5,562,510, 5,575,699, and 5,595,516 show arrangements that have been proposed for utilizing expansion chambers formed in the drive shaft housing and traps in the powerhead with catalysts contained within the expansion chamber. These devices are quite effective in achieving the various results aforenoted.
However, because of the compact nature of the structure, the aforenoted arrangements have been configured in such a way that the communication to and from the expansion chamber has not been at the optimal location.
It is, therefore, a principal object of this invention to provide an improved outboard motor exhaust system that includes an expansion chamber and trap device.
It is a further object of this invention to provide an outboard motor exhaust system of this type wherein the exhaust gases are delivered to and from the expansion chamber at locations that are substantially on its center line, and yet spaced adequately from each other to obtain full benefit of the expansion chamber.
In addition it is a further object of this invention to provide an outboard motor exhaust system wherein the trap device is located in such a way as to insure that it will be effective and will also communicate in the desired relationship to the expansion chamber.
As has been noted, it is desirable in many instances to employ a catalytic treatment for the exhaust gases. However, it is also desirable to insure that the operation of the catalyst is monitored so that if the catalyst becomes depleted or is not operating at maximum efficiency, corrective actions can be taken.
It is, therefore, a still further object of this invention to provide an engine control that employs a system for monitoring the condition of the catalyst.
It is a still further object of this invention to provide an improved catalyst sensing system for an engine control.